Battery grid alloy



BATTERY GRID ALLOY Harold E. Zahn, Buffalo, N. Y., assignor to Gould National Batteries, Inc., Depew, N. Y.

No Drawing. Application December 22, 1955 Serial No. 556,361

6 Claims. (Cl. 136-65) This invention relates to improvements in lead-acid storage battery grid constructions, and more particularly to improved alloy formulations from which such grid constructions are cast.

It has been known for some time in the art that the effective operative life of a storage battery is most often a function of the rate of deterioration of the positive grid metal. It has heretofore been considered desirable to include rather high antimony contents in grid alloys, with a view to providing the finished grid structures with adequate strength and to facilitate the grid casting processes and handling of the grids after removal from the molds. However, it is now known that high antimony contents will provide grids having relatively high rates of corrosion. Also, it is now known that as corrosion progresses, the dissolved antimony migrates from the positive plate to the negative plate, whereupon it deposits upon the negative plate as antimony metal causing spontaneous discharge of the plate by local cell action between the antimony and the sponge lead of the plate. This self discharge action takes place during periods when the battery stands idle, and thus the available battery capacity seriously decreases during periods of non-use.

Another disadvantage attendant upon antimony contamination of the negative plate, results from creation of a sulfated negative condition, as a result of the capacityrobbing self-discharge action referred to hereinabove. This condition is characterized by formation of hard granular material in the negative plate, which resists recharge to a healthy condition capable of delivering its original capacity. The hereinabove referred to disadvantages may be completely eliminated by avoiding any addition of antimony to the grid metal alloy.

Previously, attempts have been made to develop improved alloys where antimony is included in reduced amounts in an effort towards attainment of improved corrosion-resistance and reduced self-discharge rate. For example, as disclosed in Carroll Patent No. 2,694,628, grid alloys containing reduced amounts of antimony are suggested; the absence of the usual amount of antimony being compensated for by addition of materials such as tellurium, copper, etc. However, it has now been determined that whereas the objectives set forth in the aforesaid patent are probably attained to some degree, the employment of antimony and the additives referred to is otherwise undesirable for various reasons, and the resultant alloys are in any case only partially productive of the desired results.

The present invention contemplates an improved battery grid construction fabricated of an alloy free from antimony, except perhaps for trace amounts as are normally found as impurities in the lead component of the alloy. Hence, the alloy of the present invention comprising a critical formulation containing substantially no antimony, but which nevertheless possess corrosion resistance characteristics superior to the prior art formulations hereinabove referred to. Minor quantities of tin, arsenic and silver are added to the basic lead ingredient within critical atent O range ratios, such as will economically provide an improved grid alloy for reducing the self-discharge rate of the battery and increasing the grid resistance to corrosion, while at no expense to other requisite battery characteristics, such as castability of the alloy, cost of materials and fabrication, etc.

Generally stated, this invention contemplates provision of a grid metal alloy containing tin from .5 to 3.0%; arsenic from .20% to .50%, silver from .05% to .35% and lead, balance. Trace impurities of antimony, copper, bismuth etc., as usually associated with commercially pure lead are not considered as part of the alloy formulation, although their presence sometimes cannot be avoided. A preferred typical alloy of the present invention contains tin 1%, arsenic 0.3%, silver .10%, the balance lead.

It will be noted that the present invention calls for no addition of antimony to the alloy, thereby avoiding the problems referred to hereinabove in connection with excessive rates of battery self-discharging and corrosion deterioration. The tin content of the formulation of the invention operates to promote hardness of the finished grid, and also promotes by reason of its free flowing characteristics production of more uniformly solid castings, free of voids, and avoids phase segregation. The inclusion of arsenic in the formulation in the proportions specified hereinabove operates, in combination with the other components of the alloy, to produce still sounder castings, and improved weldments at junctures of colliding streams of flowing metal, through reduction of metal surface tension and disruption of the interface oxides. The arsenic component of the alloy also contributes to improve the tensile strength and corrosion resistance of the finished grid. Addition of silver as specified hereinabove to the other components of the alloy operates to still further in-v crease the corrosion resistance of the grid under condi tions such as are met with under normal battery operation. The arsenic and silver components also contribute to refine the grain structure of the alloy.

The alloy of the invention may be readily produced according to various processes well known in the art, such as by adding the alloying materials in solid form to the lead in molten form, or by adding to molten lead an appropriate quantity of lead arsenic alloy, along with solid tin and silver additions in the form of previously alloyed tin-silver-lead combinations. In practicing the invention, in one specific embodiment thereof, lead is melted in a pot and then an appropriate quantity of lead-tin alloy such as is known commercially as tin solder and comprising either a 50-50 or -40 mixture of lead and tin, as may be preferred, is then stirred into the molten lead. An appropriate amount of lead-arsenic alloy, such as is commercially available and may include from 1 to 2% arsenic, is then stirred into the molten alloy. The silver components may then be added either in the form of solid silver shot or in the form of the lead-silver alloy, such as is readily available commercially to contain from 1-5% silver; the quantities of the various alloying elements being furnished in proper proportions to form the prescribed alloy as specified hereinabove. The alloy is then heated to a temperature sufficient to insure homogeneous alloying of the components, such as for example to approximately 950 F. and is stirred or agitated to provide a uniform alloy melt. It may then be poured into suitable molds to form the grid structures of the invention, or in the alternative may be permitted to solidify in pig form for subsequent remelting and casting, as is well known in the art.

Storage batteries of generally standard production specifications incorporating grids fabricated in accord with the preferred alloy example specified hereinabove, as well as batteries containing grids of 7% antimony alloy, were 3 subjected to comparative self-discharge and over-charge tests.

The batteries werebuilt on acommercial battery production line and all processing and assembly of batteries was in accord with established production procedures.

In the self-discharge test, batteries were discharged at the 300 ampere rate after completion of building to establish their initial capacity. Duplicate batteries were allowed to stand for about 24 weeks without any attention and then discharged to measure the capacity loss resulting from the stand. The percent capacity retained given in the table below is relative to the capacity of the fresh batteries.

in the overcharge test, which is a measure of grid corrosion resistance, the batteries were subjected to a weekly cycle consisting of 999 ampere hours overcharge, followed by a 48 hour open circuit stand. Batteries were then discharged at 13 amperes for 3.5 hours or a 5.1 volt cut-off whichever occurred first. Failure was taken as occurring on that cycle in which battery voltage fell below 5.1 volts before 3.5 hours discharge at 13 amperes was complete.

' Self discharge test Thus, it will be observed that the grid alloy of the present invention provides improved self-discharge and corrosion resistance characteristics compared to previously standard type grid alloys or materials. The grids so fabricated of the alloy of the invention were observed to be of accurate size and dimension; uniformly sound and solid in form, without evidences of phase segregation or other internal or external defects; thereby demonstrat- 4 ing that the alloy of the invention facilitates the casting operation as regards accurate reproduction of mold cavities and casting soundness.

Whereas, the prior art teaches that alloys of this general type are not readily castable unless they contain antimony in appreciable quantities, it has been discovered that by the present invention an alloy free of antimony and readily castable may be produced.

I claim:

1. A storage battery grid metal alloy being substantially free from antimony and consisting essentially of from 0.50% to 3.0% tin, from .2 to 5% arsenic; from 05% to .35 silver; and the balance lead.

2. A grid metal alloy being substantially free from antimony and substantially of the following composition; tin 1%; arsenic 30%; silver .10%, balance lead.

3. In an electric storage battery including a negative plate and a positive plate having a grid being substantially free from antimony and consisting essentially of an alloy of lead, silver, arsenic, and tin containing from 0.5% to 3% tin; from .2% to .5% arsenic; from .05% to 35% silver; and the balance lead, whereby corrosion of the positive grid is minimized and self-discharge of the negative plate is opposed.

4. A storage battery grid metal alloy containing substantially no antimony and consisting essentially of from 0.50% to 3.0% tin; from .2% to .5% arsenic; from 05% to 35% silver; and the balance lead.

5. A grid metal alloy substantially free of antimony and of the following composition; tin 1%, arsenic 30%; silver .10%; balance lead.

6. In an electric storage battery including a negative plate and a positive plate having a grid containing no more than trace amounts of antimony and consisting essentially of an alloy of lead, silver, arsenic, and tin containing from .5% to 3% tin; from .2% to .5% arsenic; from .05 to .35 silver; and the balance lead, whereby corrosion of the positive grid is minimized and self-discharge of the negative plate is opposed.

References Cited in the file of this patent UNITED STATES PATENTS 2,089,939 Betterton et al Aug. 17, 1937 2,306,667 Smith et a1 Dec. 29, 1942 2,570,501 Snyder Oct. 9, 1951 2,678,341 Stoertz May 11, 1954 FOREIGN PATENTS 411,524 Great Britain June 8, 1934 

1. A STORAGE BATTERY GRID METAL ALLOY BEING SUBSTANTIALLY FREE FROM ANTIMONY AND CONSISTING ESSENTIALLY OF FROM 0.50% TO 3.0% TIN, FROM .2 TO .5% ARSENIC, FROM .05% TO .35% SILVER, AND THE BALANCE LEAD. 